This paper reports on the effects of using hardware virtual memory assists in managing file buffer caches in UNIX. A controlled experimental environment was constructed from two systems whose only difference was that one of them (XMF) used the virtual memory hardware to assist file buffer cache search and retrieval. An extensive series of performance characterizations was used to study the effects of varying the buffer cache size (from 3 Megabytes to 70 MB); I\O transfer sizes (from 4 bytes to 64 KB); cache-resident and non-cache-resident data; READs and WRITEs; and a range of application programs.